ash: Can't access tty problems (initramfs)

[Denis Vlasenko]

On Friday 18 May 2007 00:29, Hamish Moffatt wrote:
> On Thu, May 17, 2007 at 11:28:06AM -0500, Dallas Clement wrote:
> > I'm getting the infamous "Can't access tty; job control turned off"
> > message when I try to invoke the ash shell during my initial bootup.
> > 
> > I'm using busybox 1.5.0.  I also understand that ash requires a
> > controlling tty rather than the console.  Though, I don't understand all
> > the reasons.
> 
> I saw this too when I upgraded from 1.4.2 from 1.5.0, so I switched
> back. The same /dev entries work perfectly in 1.4.2. I did not have
> time/need to debug it.

I think there is nothing to "debug", as this is not a bug.
/dev/console CANNOT be a controlling tty, and code which
was trying to "fix" this was removed from init.c

The diff is a bit big:

http://busybox.net/cgi-bin/viewcvs.cgi/trunk/busybox/init/init.c?rev=17937&r1=17917&r2=17937

but the core of change is here:

 static void console_init(void)
 {
-	int fd;
-	int tried = 0;
-	struct vt_stat vt;
 	struct serial_struct sr;
 	char *s;
 
-	if ((s = getenv("CONSOLE")) != NULL || (s = getenv("console")) != NULL) {
-		safe_strncpy(console_name, s, sizeof(console_name));
-	} else {
-		/* 2.2 kernels: identify the real console backend and try to use it */
-		if (ioctl(0, TIOCGSERIAL, &sr) == 0) {
-			/* this is a serial console */
-			snprintf(console_name, sizeof(console_name) - 1, SC_FORMAT, sr.line);
-		} else if (ioctl(0, VT_GETSTATE, &vt) == 0) {
-			/* this is linux virtual tty */
-			snprintf(console_name, sizeof(console_name) - 1, VC_FORMAT, vt.v_active);
-		} else {
-			strcpy(console_name, DEV_CONSOLE);
-			tried++;
-		}
+	s = getenv("CONSOLE");
+	if (!s) s = getenv("console");
+	if (s) {
+		int fd = open(s, O_RDWR | O_NONBLOCK | O_NOCTTY);
+		if (fd >= 0) {
+			dup2(fd, 0);
+			dup2(fd, 1);
+			dup2(fd, 2);
+			while (fd > 2) close(fd--);
+		}
+		messageD(L_LOG, "console='%s'", s);
 	}
 
-	while ((fd = open(console_name, O_RDONLY | O_NONBLOCK)) < 0 && tried < 2) {
-		/* Can't open selected console -- try
-			logical system console and VT_MASTER */
-		strcpy(console_name, (tried == 0 ? DEV_CONSOLE : CURRENT_VC));
-		tried++;
-	}
-	if (fd < 0) {
-		/* Perhaps we should panic here? */

See those now-removed ioctls and then 'while ((fd = open(console_name...' ?
This is the code which tried to close '/dev/console' and open
'/dev/ttyN' or '/dev/ttyS0' instead.

This is just WRONG. init should not do it. It should just use file
descriptors 0, 1, and 2 which were given to it by kernel.
--
vda